At least 70 people in Guangdong province have suffered food poisoning over the past three days after eating pig organs contaminated by a banned food additive, the local health authority said over the weekend.

Three people remain in hospital for observation while the remaining have been discharged after treatment, said Wang Guobin, an official with the Guangzhou municipal public health bureau.

The victims complained of stomach ache and diarrhea after eating pig organs bought in local markets since Thursday, Xinhua News Agency reported. All of them were from the Tianhe and Zengcheng districts of Guangzhou, capital of Guangdong, the authorities said on Saturday.

Wang said initial investigations show that the pig organs were contaminated by clenbuterol, an additive that is banned in pig feed in China.

Three people have been detained for suspected involvement in raising and selling the contaminated pigs. Local authorities have found that the contaminated pigs came from farms in several places in Hunan province.

Clenbuterol, dubbed "shouroujing", can prevent pigs from accumulating fat, but is harmful to humans and can be fatal. Clenbuterol residue often accumulates in organs such as the liver and lungs. One of the largest food poisoning cases involving clenbuterol happened in Shanghai in September 2006 when 336 people were hospitalized after eating pig meat or organs contaminated with the additive.